Ping in emulation takes only one direction delay if you have set only one application with Ping Source IP and ping Destination IP. This is because PING is a two-way application and constitutes PING_REQUEST and PING_REPLY. For ping to take round trip delay users must configure two Emulation Applications, one for forwarding PING_REQUEST and other for the reverse PING_REPLY.

For Eg: If you are running a ping from the IP to an IP the time taken will normally be around 1ms.

Now we create a network scenario in NetSim similar to the screenshot shown below, 

we reset the propagation delay in both the wired links to 5 ms.

We configure an Emulation application between the wired nodes with the source and destination real IP specified, as shown below:

On running the simulation, you will observe the variation in the time taken to get the ping reply in the source system, as shown below:

Ping packets have experienced an additional delay of 10ms which is a sum of the delay in both the links.

The additional delay experienced by ping packets is not 20ms because the application that we have configured applies to only the Ping Request packets which have the Source IP as and Destination IP as

The Ping Reply Packets has the Source IP as and Destination IP as, for which we have not configured any application.

For the ping to take the round trip delay, we will have to configure one more application for the reverse traffic. On adding an application for the reverse traffic as shown below:

We will now be able to see round trip delay being experienced by the PING application, as shown below:

Ping experiences an additional overall delay of 20ms, which is the sum of the delay's experienced by Ping Request and Ping Reply (10ms + 10ms).